Cellular phenotype is the conglomerate of multiple cellular processes involving gene and protein expression that result in the elaboration of a cell's particular morphology and function. It has been thought that differentiated post-mitotic cells have their genomes hard wired with little ability for phenotypic plasticity. Emerging evidence has, however, demonstrated the reversibility and flexibility of the cellular phenotype. It has been shown that fertile adult male and female frogs can be obtained by injecting endoderm nuclei into enucleated eggs (Gurdon J B, Elsdale T R, & Fischberg M (1958) Sexually mature individuals of Xenopus laevis from the transplantation of single somatic nuclei. Nature 182(4627):64-65). This result not only forms the foundation of the field in nuclear transplantation, but also provides evidence that the cytoplasmic components of a differentiated cell can support nuclear reprogramming. Generation of induced pluripotent stem (iPS) cells by transfection transcription factors into dividing fibroblasts (Takahashi K & Yamanaka S (2006) Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell 126(4):663-676), followed by cell selection represent a new strategy to globally revert a mature cell into a different cell type. See: Huangfu D, et al. (2008) Induction of pluripotent stem cells from primary human fibroblasts with only Oct4 and Sox2. Nat Biotechnol 26(11):1269-1275; Kim J B, et al. (2008) Pluripotent stem cells induced from adult neural stem cells by reprogramming with two factors. Nature 454(7204):646-650; Nakagawa M, et al. (2008) Generation of induced pluripotent stem cells without Myc from mouse and human fibroblasts. Nat Biotechnol 26(1):101-106; Maherali N, et al. (2007) Directly reprogrammed fibroblasts show global epigenetic remodeling and widespread tissue contribution. Cell Stem Cell 1(1):55-70; Okita K, Ichisaka T, & Yamanaka S (2007) Generation of germline-competent induced pluripotent stem cells. Nature 448(7151):313-317; and Stadtfeld M, Nagaya M, Utikal J, Weir G, & Hochedlinger K (2008) Induced Pluripotent Stem Cells Generated Without Viral Integration. Science 322(5903):945-949. The need for re-differentiation of these ES-like-iPS cells into desired cell types, however, adds a layer of complexity that is difficult to control (Wernig M, et al. (2008) Neurons derived from reprogrammed fibroblasts functionally integrate into the fetal brain and improve symptoms of rats with Parkinson's disease. Proc Natl Acad Sci USA 105(15):5856-5861; Hanna J, et al. (2007) Treatment of sickle cell anemia mouse model with iPS cells generated from autologous skin. Science 318(5858):1920-1923). Nevertheless, studies of nuclear reprogramming from genomic and epigenetic modification, as seen from somatic-cell-nuclear-transfer-cloned animals and iPS cells, suggests the flexibility of a differentiated phenotype as well as the dynamic changes of a genome (Maherali N, et al. (2007) Directly reprogrammed fibroblasts show global epigenetic remodeling and widespread tissue contribution. Cell Stem Cell 1(1):55-70).
Despite the development and refinement of the techniques discussed above, there remains a need in the art for methods and compositions for effecting phenotypic change in a cell. This invention addresses that need.